Chemical reagent



atented Feb. 11, 193% FRED H. RHQDES, F ITHACA, NEW YORK CHENIICAL REAGENT No Drawing. Application filed July 18,

The invention relates to inhibitors or restrainers useful in chemical and electrochemical processes for preventing or retarding the evolution of hydrogen at the surfaces of metals immersed in the solution or for otherwise preventing or retarding the chemical action of acids on metals. The invention is particularly applicable to chemical processes wherein metals such as iron, steel, nickel, etc'., are subjected to the action of acids for removing scale, rust or oxide from the surfaces thereof. Such processes are often referred to as pickling processes and are widely used in manufacturing establishments.

My invention consists in the discovery of a series of chemical compounds which when added to certain chemical reagents act to inhibit the undesired reactions of said reagents without interfering with the desired reac- 0 tions thereof. For instance when added to a pickling bath of a composition that would ordinarily have a corrosive action upon metals, such compounds serve to retard the corrosive action on the metals and the consequent evolution of hydrogen without interfering materially with the desired function of dissolving the oxide, rust or scale found on the surface of the metal.

There are many advantages in the use of a pickling bath having incorporated therein an inhibiting agent for retarding the chemical action of the acid on the metal. For example, such acomposition is useful in removing the layer of iron oxide which is formed on steel or iron during the rolling of sheets, the drawing of wires or rods, the spinning of thin shapes and the annealing of shapes prior to an application of a coating of vitreous enamel, glass, tin, zinc or other metal or paint, varnish enamel, lacquer or other protective or decorative coating. Another use of the process is in the removing of the metallic oxide or carbonate forming on copper or other non-ferrous materials. Another advantageous use is in eliminating the scale forming in pipes and in the tubes of automobile radiators which often seriously interferes with the proper flow and circulation of the fluid through the radiator. My 5 invention is applicable generally to the re- 1929. Serial No. 379,320.

moval of oxides and scales from metals by a pickling'process and the use of the inhibiting agents not only prevents or diminishes the attack of the metals themselves by the acid but also creates more healthful working conditions surrounding the pickling bath. The evolution of hydrogen gas, which is an incident of the attack of the metal by the acid, results in the carrying into the surrounding air of a certain amount of the acid of the bath in the form of a spray which is injurious to the1 operators and wasteful of the acid materia In its broader aspects, my invention contemplates the use of the inhibiting agents hereinafter more fully described in connection with any chemical or electrochemical solution or reagent which under normal conditions of operation will evolve hydrogen at the surface of a metal immersed therein. In other words, my invention provides a means for causing desired chemical or electrochemical reactions to take place and without substantially decreasing the rate of said reactions causing an inhibiting action retarding or actually preventing the evolution of hydrogen which would normally take place without the presence of the inhibiting agents.

As a further example of the utility of my invention, it may sometimes be found desirable to use the new inhibiting agents in connection with electroplating processes. It is well known that in the electrodeposition of certain metals hydrogen is liberated at the cathode in addition to the metal which it is desired to plate. By using the inhibiting agents in accordance with my invention the evolution of hydrogen at the cathode may be retarded without correspondingly retarding the deposition of the metal. Thus the efticiency of the plating process is increased and certain undesirable characteristics of the plated metal caused by the evolution of hydrogen may be eliminated.

The new inhibiting agents which I have discovered may be broadly classified as cyclic organic compounds in which a ring of atoms containing at least one atom of nitrogen 1s attached to at least one nucleus containing at least two rings of atoms. I have found that compounds which may be broadly described as above are particularly desirable for use as inhibiting agents and are very effec tive in preventing or retarding the evolution of hydrogen. While there are a number of compounds coming within the purview of this invention, I will refer more specifically a-B dinaphthacridine Fluorenenaphthacridine 6-3 qinaphthacrldine in the form of a salt as,

The compounds mentioned above may ordinarily be used as inhibiting agents either in the pure state or in the relatively impure form resulting from commercial methods of manufacturing the same. It has been found that in many cases the impure compounds are more efficient inhibitors than the chemically pure substances. This may possibly be due to the presence of small amounts of more complex derivatives in the impure material. The inhibiting compounds may be introduced into the chemical reagent not only in the form of a free base as indicated in some of the formulas given above, but may also be used for example, the hydrochloride of the base.

The amount of the inhibiting agent to be used for any given chemical solution depends not only upon the efiiciency of the inhibiting agent but also on operating conditions and the exact results desired in the particular process. In general it may be said that with the compounds mentioned above as the inhibiting agents, 1% or less of the compound added to the solution will be sufiicient to obtain the maximum effect although there is apparently no disadvantage other than increased cost' in adding larger amounts if so desired. There is, however, a certain relation and its efficiency.

For example it has been found that when ,8 naphthoquinoline is added to a pickling bath containing 7.5% sulphuric acid, there will be an inhibiting action to the extent of 91.2% when 10 millimols per liter is introduced at 60 (land there will be an inhibiting action to the extent of 95.9% when 100 millimols of the same substance is used per liter of solution under otherwise similar conditions.

It has also been found that the introduction of a saturated solution of diphenanthracridine obtains an inhibiting action of 96.6%.

The amount of inhibiting action desired may vary for different manufacturing conditions. For example, in pickling thin sheet steel for light enameled ware it is desirable to use sufiicient inhibitor to effect as much as 98% inhibition, whereas in pickling thicker sheets for heavy enamel as little as 80% inhibition might be desired. Thus according to my invention, the inhibiting agent may be added in amounts sufficient only to retard the evolution of hydrogen or on the other hand a suitable inhibiting agent of high efficiency may be added in larger amounts in -a dinaphthacridine Diphenanthracrldine order to substantially prevent the evolution of hydrogen.

From the above description it will be noted that my invention relates to the discovery of a series of cyclic organic nitrogen compounds having inhibiting characteristics rendering them very valuable. in chemical and electrochemical processes with which they have never heretofore been associated. While I between the amount of inhibiting agent added i nmaevo have described certain compounds and certaln processes with particularity, it is to be understood that the invention is not necessarily limited thereby except in the light evolves hydrogen at the surface of a metal immersed therein and an inhibitor or restrainer in said solution for diminishing the evolution of hydrogen comprising an acridine nucleus having attached thereto at least one additional six membered ring composed of carbon atoms.

3. A liquid bath for chemical or electrochemical purposes comprising a solution which under normal conditions of operation evolves hydrogen at the surface of a metal immersed therein and an inhibitor or restrainer in said solution for diminishing the evolution of hydrogen comprising an acridine nucleus having an additional ring of atoms attached to two carbon atoms of said acridine nucleus.

4. A liquid bath for chemical or electrochemical purposes comprising a solution which under normal conditions of operation evolves hydrogen at the surface of a metal immersed therein and an inhibitor or restrainer in said solution for diminishing the evolution of hydrogen comprising an acridine nucleus having an additional ring of atoms, said ring containing six carbon atoms of which two are common to both the acridine nucleus and the said ring.

consists in introducing into the li uid reagent an acridine nucleus having an ad 'tional ring of. atoms, said ring containing six carbon atoms of which two are common to both the ring and said acridine nucleus.

In testimony whereof I afiix my signature.

FRED H. ,RHODES.

5. The process of inhibiting or restraining the evolution of hydrogen at the surface of a metal immersed in a liquid reagent which consists in introducing into the liquid reagent dinapthacridine.

6. The process of inhibiting or restraining the evolution of hydrogen at the surface of a metal immersed in a liquid reagent which consists in introducing into the liquid reagent an acridine nucleus having attached thereto at least one additional six membered ring composed of carbon atoms.

7. The process of inhibiting or restraining the evolution of hydrogen at the surface of a metal immersed in a liquid reagent which consists in introducing into the liquid reagent an acridine nucleus having an additional ring of atoms attached to two carbon atoms of said acridine nucleus.

8. The process of inhibiting or restraining the evolution of hydrogen at the surface of a metal 1. .1 ersed in a liquid reagent which 

